The present invention relates generally to a pressure transducer apparatus and, more particularly, to a pressure transducer protection apparatus for severe environments.
The state of the art of pressure transducer protection apparatus is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,024,649 issued to Taber on Mar. 13, 1962;
U.S. Pat. No. 3,706,953 issued to Kicks et al on Dec. 19, 1972; and
U.S. Pat. No. 4,686,746 issued to Adams et al on Aug. 18, 1987.
The Taber patent is directed to a force measuring instrument having a flexible fluid and vapor barrier for transmitting force to means sensitive to force and variations thereof. The instrument has pressure sensitive potions formed to engage and support the central portion of the barrier while the barrier has a bead section connecting the central section to the marginal portion.
The Kicks et al patent discusses a protected pressure transducer having such a flexible diaphragm as the pressure sensing means, the diaphragm is mounted within a tubular housing which incorporates a protector plate fitted across the entire cross-sectional area of the tubular housing and it is formed with a plurality of holes near its circumference with all these holes being radially spaced beyond the circumference of the diaphragm to direct the fluid stream, possibly carrying particles, to energy absorbing structure located radially beyond the circumference of the diaphragm.
The Adams et al patent describes a solid state semiconductor pressure sensor in which the pressure sensor element is protected from the ambient whose pressure is being measured by a combination of a pressure transfer medium and a thin covering membrane. A method is described for applying the thin covering membrane so as to substantially avoid entrapment of air or formation of voids in the pressure transfer medium which would degrade the performance of the sensor. The pressure transfer medium is gel-like material such as a silastic.
The problem solved was to measure air loads plus dust loads in transient dusty flow behind a simulated nuclear air blast. The gauge design requirements were to survive for more than 100 milliseconds in a dusty flow environment that included particle sizes up to 1 mm and particle velocities up to 2200 fps. The design pressure range was 150 psig nominal with pressure spikes up to 300 psig resolution. The accuracy goal was 3 psi at pressure levels from 0 to 50 psig. The response goal was to fully respond to pressure changes within one millisecond. The gauges had to be small enough to be easily installed in subscale models. The exposed material subjected to the environment had to be similar to the model surface so that the dust interaction with the surface was similar. Gauges produced generally exceeded design requirements and goals.
While this concept was developed for a specific application, it could be used in other erosive, corrosive or high temperature environments where high frequency measurements are to be made.
Prior attempts to measure dust and air loads were marginally successful at best. The use of pressure transducers without protection usually resulted in gauge destruction before the desired data were obtained. Protection devices often caused interference and non-linear effects, which produced erroneous results. Also, those gauges often had baseline (zero) shifts and drifts that were larger than desired measurements. Larger mechanical devices generally had slow response, were cumbersome from the standpoint of installing in models, and required considerable analysis and interpretation of the results, which were generally still open to question.
While the above-cited references are instructive, there still remains a need to provide a pressure transducer protective apparatus for operation in severe and harsh environments. The present invention is intended to satisfy that need.